1. Field of the Invention
The present invention relates to a method of forming electrical leads on a semiconductor device and to the structure of the leads and, more particularly, to a method of forming joints between first and second leads as well as to the structure of the joints between the leads.
2. Description of the Prior Art
In the past, first and second leads have been connected together on a semiconductor device in the manner to be described below. After forming a first metal layer for creating first leads, an insulating film is formed on the metal layer. Then, holes (hereinafter referred to as the contact holes) are formed in the insulating film. Subsequently, a second metal layer for creating second leads is formed by sputtering. The contact holes are created to make electrical connection between the first and second leads. In order to facilitate formation of the second leads within the contact holes and to prevent the thickness of the leads from decreasing in the contact holes, the semiconductor substrate is heated during the sputtering process, or the side walls of the contact holes in the insulating film ar sloped.
In the aforementioned prior art techniques, however, as the sizes of the contact holes decrease, it becomes more difficult to prevent the second metal leads from thinning in the holes even if the semiconductor substrate is heated. In the worst case, the second metal leads break, or it is impossible to make electrical connection of the second metal leads with the first metal leads. Where the side walls of the contact holes in the insulating film are tilted, or sloped, the wiring of the second metal leads is improved, and the leads can be prevented from breaking. However, for a given area with which the first and second leads are in contact with each other, the size of the upper end of each contact hole is increased due to the tilt of the side walls. This makes it impossible to fabricate the semiconductor device in a smaller size.